1. Field of the Invention
The present invention relates to a control apparatus for a suction air quantity of an engine capable of controlling a suction air quantity of an engine in case of a misfire or the like.
2. Discussion of Background
A control apparatus for a suction air quantity of an engine of this kind is well known wherein the suction quantity to an engine is controlled by changing an opening area of a passage which bypasses a throttle valve. In this apparatus, especially, to stabilize a revolution number of an engine in idling time, the suction quantity of air in the bypass passage corresponding with the temperature of the engine by an open loop control. In this apparatus after detecting the throttle valve is fully closed by an idling switch and the like, the revolution number of the engine is controlled by a feed back control to a target revolution number. It is generally well known that a suction quantity control is carried out to correct timewise change by this feed back control of the revolution number.
No description has been made on the protection measure for a misfire of the engine in this conventional apparatus.
The conventional control apparatus for a suction air quantity of an engine composed as above has a problem wherein, when one cylinder of, for instance, a four cylinder engine is misfired in idling time, the revolution number of the engine rapidly drops after the misfire, and the engine may have an engine stall.
Even if the engine does not have an engine stall, the revolution number of the engine is controlled by a feed back control system with the residual three cylinders, which requires a considerable time until the revolution number of the engine reaches a predetermined revolution number, that causes the instability of the rotation of the engine during that period.
Moreover, when the revolution number of the engine reaches a predetermined quantity in misfire time, if a suction air control to correct the timewise change, so called a learning control, is carried out, and if the misfire is temporary and stops happening, the suction quantity becomes so large that the revolution number of the engine becomes higher than the predetermined revolution number.